The present invention relates to a method of and an apparatus for operating a display screen, and more particularly to a method of and an apparatus for controlling a display device which is used for displaying a logical screen different in size from a physical screen and which has a function of zooming a displayed image.
In a display device for displaying a logical screen larger in size than a physical screen, only part of the logical screen is displayed on the physical screen. In this case, when it is indicated by one of input devices such as a keyboard and a pointing device (hereinafter referred to as "mouse") that a displayed area is to become narrower, an enlarged image of a character or figure is displayed on the physical screen. When the enlarged image is displayed, a displayed area of the logical screen corresponding to the physical screen becomes smaller than an initial displayed area of the logical screen. As a result, in some cases, a desired character or figure may vanish from the physical screen. In such cases, for example, a method has hitherto been used which is described in a Japanese Patent Application JP-A-55-78335. In this method, the displayed area is continuously moved in a desired direction until the desired character or figure is displayed on the physical screen.
In the above method, however, there arise three problems, a first one of which is that a zooming operation command and a displayed-area moving command are separately issued, and thus the number of operations increases. A second problem is that an operation is required to issue each of the zooming operation command and the displayed-area moving command a plurality of times till a desired area on the logical screen is displayed on the physical screen. This is because an enlarged or contacted image may be displayed in a state that the moving distance necessary for reaching the desired area on the logical screen is erroneously estimated or the movement for reaching the desired area on the logical screen is forgotten. A third problem is that it is required to display a plurality of areas of the logical screen on the physical screen till the desired area of the logical screen is displayed, and hence the amount of processing executed by a computer and the processing time thereof are increased.